v-Src has been studied as a model oncogene for over 25 years and it is still unclear which substrates contribute critically to its ability to tranform cells. We recently identified LRPI as a Shc associated protein in v-Src transformed cells. Upon tyrosine phosphorylation LRP1 associates with Shc and possibly other signaling proteins. These observations led to a model in which Shc is recruited to the plasma by binding to LRPI. It is at the membrane that Shc is thought to be involved in Ras activation. This grant is aimed at understanding the role of Shc and LRP1 in cellular transformation by v-Src. In addition, we propose to identify novel v-Src substrates. Identification of substrates that play an important role during cellular transformation is important because it will lead to new insights into this process. In addition these substrates provide targets for intervention. To find out whether either Shc or LRP1 are important during transformation by v-Src we will analyze the ability of v-Src to transform Shc-deficient and LRPl-deficient cells. To investigate how Src selects LRP1 as a substrate, we will mutate the different domains in Src and ask which of them are essential for the tyrosine phosphorylation of LRP1. Preliminary evidence suggests that Shc binds to one or more LRP1 isoforms. We propose experiments to identify those isoforms. Finally we propose purify and identify novel v-Src substrates.